The present invention relates generally to foam-in-place packaging. Foam-in-place packaging has been well known and widely used as a protective packaging method for a number of years. The underlying technology is based upon the reaction between two (usually liquid) chemicals that form a solid polymer while at the same time generating a gaseous byproduct. In particular, when isocyanate compounds react with polyols and water, the reaction produces both a urethane polymer ("polyurethane") and carbon dioxide. Under proper conditions, the carbon dioxide generated by the reaction will bubble and disperse through the polymer as it hardens to thus form an expanded polymer foam that can be used as a protective material for packaging fragile objects. The process by which the liquid precursors mix as liquids and then expand as not-yet-hardened foam takes about 20-30 seconds, thus making feasible its manipulation and use for packaging purposes.
In a first generation of foam-in-place packaging, objects to be protected were placed into containers (e.g. corrugated boxes), and wrapped or draped with a protective material such as a plastic sheet. Thereafter, the polyol component and isocyanate component were pumped from separate supplies, mixed, and then injected from a gun-like dispenser into the container. If the amount of injected mixture was appropriate, the resulting foam would essentially fill the interior of the container while surrounding the object to provide a custom package. Such relatively straight forward injection practices are still useful in many applications, and an updated injection device is disclosed, for example, in copending and commonly assigned application Ser. No. 08/361,322 filed Dec. 21, 1994 for "Hand Held Dispenser for Foamable Compositions and Dispensing System."
In a next generation of foam-in-place packaging, devices have been developed which concurrently produce plastic bags and fill them with the foamable mixture of polymer precursors. The bag has a vent to permit the carbon dioxide to escape. A packaging operator can simply drop one or more newly made bags into a container carrying an object to be packaged, and then close the container. The foam in the bags continues to expand until it likewise fills the interior of the container while forming a custom-shaped cushion around the object packaged therein. Such bag making systems provide the advantage of injecting the foam into a bag that is immediately closed, rather than requiring the operator to manually dispense the foam. As is known to those familiar with such foamable chemicals, they tend to be extremely messy and, if not controlled properly, can cause problems which slow or stop the entire packaging process until the unwanted foam residue can be cleaned up. In more serious circumstances, the foam can even cause its handling machinery to break down leading to further additional delays.
Examples of foam-in-place devices are described in a number of patents and copending applications that are commonly assigned with the present invention. These include inter alia, U.S. Pat. Nos. 4,800,708; 4,854,109, 4,938,007; 5,027,583; 5,139,151 and 5,376,219 and pending applications Ser. No. 08/121,751, filed Sep. 15, 1993 and Ser. No. 08/514,010 filed Aug. 11, 1995.
The packaging requirements of various users can, however, differ widely. Thus, any particular given foam-in-place system may not be appropriate or economically viable for every potential user. For example, users who repetitively use foam cushions on a large volume basis are probably most appropriately served by one of the more sophisticated devices such as those described in U.S. Pat. Nos. 5,376,219 or 4,800,708. For less frequent users, the smaller and more compact devices such as that illustrated in pending applications Ser. Nos. 08/121,751 and 08/514,010 may be appropriate, and as mentioned above, some users still prefer the simplest technique of using an injection system with a gun type device that dispenses the foam.
At present, however, the market lacks any foam-in-place packaging system for the less frequent user who would otherwise like to take advantage of foam-in-place packaging, but has neither the desire nor the facilities to incorporate any one of the previous mentioned foam-in-bag systems. Accordingly, it has been considered desirable to manufacture a bag in which the foam precursors are separately maintained during storage so that in use, the packaging operator can simply take one of the bags, mix the ingredients by hand (i.e. handle the bag's exterior while mixing the precursors inside), and then place the expanding bag and foam into a package for purposes identical to those just described.
To date, however, attempts at doing so have been generally unsuccessful for reasons that are best illustrated by U.S. Pat. No. 3,419,134 to Fitts, and U.S. Pat. No. 4,232,788 to Roth.
Fitts '134 discloses several variations of a foamable package and a method for forming cellular foam in which the foam precursors are placed in two separate smaller bags inside a larger bag. According to Fitts, there are rupturable walls between the bags, so that when the operator physically breaks the walls, the chemicals will mix and form foam. The Roth '788 disclosure is essentially the same from a conceptual standpoint. Each of these suffer from some significant disadvantages, however, and essentially neither has appeared on the marketplace in any significant presence.
There are several reasons for this failure. First, in order to produce foam, the two foam precursors must mix successfully and completely. Indeed, the successful total mixture of the foamable precursors is a fundamental requirement for all foam-in-place systems. Stated differently, if the foam precursors fail to mix successfully, either foam will not be produced, or the foam that is produced will be structurally inappropriate.
Thus, the Fitts disclosure demonstrates that in the bag-in-bag structure, some residue of at least one, and sometimes both, of the precursors will always tend to remain behind and unreacted on the inner walls of the separate bags. In turn, the presence of this residue raises several problems. First, the foam precursors (particularly the isocyanates) are environmentally undesirable and subject to regulation as such. In fact, they are much more undesirable than is the polyurethane foam, which is much more environmentally friendly. Thus, use of a Fitts-type bag will often result in a packaging cushion that contains some residual isocyanate, and quite possibly an inferior foam as well. Additionally, the isocyanate residue could potentially damage items being packaged that were chemically sensitive to isocyanate.
Secondly, because the Fitts and Roth-type devices often fail to permit all of the precursors to react with one another, the yield of foam is typically reduced, thus reducing their packaging effectiveness and cost efficiency. The failure to permit the precursors to react completely can also produce an "off-ratio" foam with less satisfactory--or even failure-prone--properties.
Third, in some of the Fitts-type devices, foam is essentially forced to break out of the second bag. As known to those familiar with foamable compositions, foam is best produced when it is allowed to properly expand and form within the packaging container. Foam that can't properly expand--and foam in a Fitts-type device typically will not properly expand--will lose yield and efficiency (i.e. less cubic feet of foam per pound of chemicals), will have a deficient cell structure (causing the foam to perform less properly than it otherwise could or for which it was designed), and will tend to shrink causing similar problems.
Accordingly, the Fitts and Roth devices will either have unreacted residue, or will restrict the desired expansion of the foam, or both.
As yet another disadvantage, the chemicals used to make foam are generally very sensitive to atmospheric conditions, and if exposed to atmospheric conditions, their effectiveness will be reduced or destroyed. In particular, when exposed to ambient conditions isocyanate precursors will tend to crystallize, while the polyol component will tend to lose water through evaporation, thus minimizing the effectiveness of each. Therefore, the "shelf life" of prior devices has been considerably less than is desirable.
The Fitts disclosure dates from approximately 1965, and those of ordinary skill in the art of plastics making and sealing will recognize that seals that are rupturable upon demand within such bags were generally not then available on any commercial basis, or indeed any basis at all, at the time of the Fitts disclosure.
Both Fitts and Roth demonstrate their lack of a proper understanding of the necessary relationships between and among plastic film and foam precursor technology. For example, Fitts suggests that "plastic film material" (Column 3, lines 56-70) is suitable, when in fact the great majority of ordinary plastic films are entirely too permeable to water-vapor or other gases to provide any reasonable shelf life for isocyanate foam precursors. Similarly, Roth suggests that his disclosed bag and precursor-containing "sachets" can be formed by heat-sealed polyethylene or polypropylene, when in fact both polymers--standing alone--are difficult to form into seals or pouches that will tear or rupture in the controlled fashion necessary for practical shelf-storable foam-in-place bags. Heat-sealed polyethylene has a relatively high burst strength, and rarely tears in a controlled or planned manner.
Therefore, there remains the need for a foam-in-place bag system which the end user can keep in shelf storage for an appropriate period of time and which, when it is to be used, can be easily internally ruptured to give a complete mixing of the foam precursors that eliminates precursor residue and allows proper expansion of the foam in order to form a structurally appropriate packaging cushion.
Furthermore, based on the usefulness of the bag precursors described and claimed in the '981 parent application, it has been discovered that various enhancements can increase such usefulness even further. Such enhancements are set forth in the following copending applications, all of which are filed concurrently herewith: Ser. No. 08/843,275 (abandoned) for "Gas Permeable Foam In Bag Packaging System;" Ser. No. 08/838,881 for "Foam In Bag Packaging System For Manual Use;" and Ser. No. 08/834,636 (abandoned) for "Thermally Insulated Foam In Bag Packaging Cushion." All three of these copending applications are incorporated entirely herein by reference.